The laser perforation technique (e.g., system(s), device(s), process(es), etc.) can satisfy various requirements of porous films as put forward in various industries. For instance, the disclosed laser perforation technique can provide control of pore dimensions and/or distributions with ease of implementation, controlled speed of formation, and substantive process integrity.
The laser perforation technique has been used previously to prepare thin, porousfilms with a well-controlled porous morphology. For example, U.S. Pat. No. 7,083,837 describes the use of the laser perforation technique using a CO2 laser to prepare packaging films. The controlled pore morphology allows to tune the oxygen transmission rate (OTR), moisture vapor transmission rate (MVTR) and the CO2 transmission rate (CO2TR). The targeted pore sizes are in the range of 110 to 400 micrometers. In another example, DE 19647543 describes the use of the laser perforation technique to prepare packaging films with non-spherical holes, which deform as a function of the applied stress. Another example, EP 0953399, shows that the same laser perforation method can be used to create perforated films with an even larger pore size of up to 5000 micrometers. In another example, JP 10330521, the laser perforation technique is used to perforate 10-120 micrometer holes in polyolefines, which comprise a high liquid (paraffinic) retention. U.S. Pat. Appl. Pub. No. 2003/0188428A1 provides examples of the application of removable films for the manufacturing of circuit boards through the laser perforation technique by using a third harmonics YAG solid-state laser with short wavelengths. Laser perforation has also been used to produce filtration membranes, for example, as described in WO1998030317A1, or drug delivery membranes, as described in WO2002081097A1, or, after filling the pores with a polymer electrolyte or fibrous fillers, as solid polymer electrolyte membranes for fuel cells, as described in WO2007011050A1, WO2007011054A1, US20060065521A1, US20060183011A1, JP2004247123, JP2009045911 and JP2009051872. The latter describes the need of cooling the polymer film during laser perforation as to prevent the polymer film from melting or dripping. In another example, US Pat. Appl. Pub. No. 2012/0244412, the laser perforation technique is used to perforate thin polymeric or metallic films of less than 20 micrometer in thickness with pores of 50 to 250 micrometer by using CO2 laser in combination with materials absorbing wavelengths in the near infra read region. After lamination of the perforated film with another porous medium, the laminate can be applied as a battery separator. JP2001319635 describes the use of a laser perforation method to perforate polyolefin films (such as polyethylene or polypropylene) of 5-30 micron in thickness. These perforated films are then combined with a fibrous polyolefin layer and applied as a battery separator. The laser perforation method and the resulting pore sizes are not described. CN101552328 describes the laser perforation of polypropylene/polyethylene/polypropylene tri-layer films, resulting in 50-400 micron large pores and a total void content of 40% or higher. Laser perforation can also be used to perforate materials other than thermoplastic polymers. For example, inorganic materials can be perforated, as e.g. described in US 2011/0262693, where an excimer laser and near-field imaging is used to laser-perforate silica films. Also, stretchable, elastomeric materials can be laser-perforated with pores of about 50 micron, as e.g. described in U.S. Pat. No. 5,336,554. WO 2008/102140 provides an example of how a laser perforation method can be applied in a continuous, on-line fashion to perforate films, although the obtained structures and properties of the films are not disclosed.
Although the use of laser perforation has been demonstrated to be useful for the preparation of well-controlled, porous morphologies in polymeric and inorganic films, there exists a need to perforate thin, polymeric films with pores that are substantially smaller than 50 micrometer in order to assure the physical separation of electrodes in energy storage devices such as batteries, electrolytic capacitors and fuel cells.